The present invention relates to oil-water separation, and more particularly, to a small, compact apparatus designed to skim a layer of oil from an aqueous surface, usually a thin film resting on top of the water in an immersion tank, such as a hot tank or the like.
When skimming a thin film of oil or grease from the top surface of the water in an aqueous parts cleaner system, there are a number of problems commonly encountered. First, the skimmer must be designed so as to float on top of the water, but more importantly, to float at almost exactly a desired level. This is to insure that, under most conditions, only a very thin layer of water, and the oil resting on top thereof, be skimmed off. While the action of floating itself is not ordinarily a problem, especially with hot tanks and the like, the temperature of the water in immersion cleaners can vary considerably. It is not uncommon to find a variety of operating water temperatures of from 100xc2x0 to 110xc2x0 up to 180xc2x0 or more. Even those baths that are intended to be carefully controlled have water temperatures that may fluctuate between 130xc2x0 and 165xc2x0 F., for example.
Consequently, assuming that a device has a body and an inlet that is intended to operate at exactly a certain level of submergence to skim the oil from the surface of the water, in other words, to have an exactly intended xe2x80x9cskim gapxe2x80x9d, thermal expansion of the floating body must be taken into account. If, for example, the skim gap is set at a certain dimension, say {fraction (7/64)}xe2x80x3, an increased water temperature will result in lower water density. This causes the floating body of a fixed volume and weight to sink down a slight amount, thereby increasing a preset skim gap.
Assuming there is a thin layer of oil on the water surface, enlarging the skim gap in turn would result in drawing an excess of water relative to oil into the collection tube. On the other hand, a reduction in temperature of the aqueous bath would cause the density of the aqueous bath to rise. This would cause the float to rise to a level whereby, in an extreme case, the skim gap would be entirely eliminated. Consequently, it would be desirable to have a floating skimmer which would be relatively insensitive to changes in temperature, at least throughout a significant range of the temperatures likely to be encountered in use.
Operating the aqueous bath in a narrow range of temperature, however, is not as easy as it may appear. This is because, in the case of some parts which are both massive and relatively cold, placing them into a heated immersion tank would lower the temperature considerably. The thermostat, although attempting to control the temperature, is still faced with a rather substantial induced variation in temperatures, at least in the short run. Furthermore, the materials from which the present skimmer is made obviate any problems with operating a hot tank at temperatures up to 180xc2x0 F., for example.
The configuration of certain embodiments of the present invention is also important. This configuration is such that there is provided a horizontal inlet into the body within a recess formed by contoured side walls and, preferably a flat bottom shelf. The oil to be separated by the surfactant forms a relatively thin film on top of the water, in most cases. In some cases, of course, the oil film may be very thick at the beginning of a new cycle, however, within a short time it again assumes the dimensions of a thin film.
It is thought that when a thin layer of oil atop a layer of water passes through a skimmer""s horizontal inlet, the water may cling to the lower shelf and establish a Prandtl boundary layer whose velocity gradient effects a certain amount of separation by retarding the flow of water relative to the oil layer.
Other considerations include the skim gap whose optimum value will vary depending, among other things, upon the type of pump used to remove the skimate. For example, a {fraction (7/16)}xe2x80x3 skim gap was found to work well with a bellows pump pumping at one pint per minute.
The skim gap is relatively critical and the float and weight construction of the present invention makes it easy to maintain such a relationship. Consequently, with a properly designed skimmer, substantial amounts of oil pass into the collection tube, and these can be readily removed therefrom by a pump.
In addition, it has been found that the body of the skimmer preferably should be located in a corner of the hot tank, inasmuch as, in most cases, convection currents caused by the heater generally favor flow of the oil film into a corner of the bath. Consequently, the skimmer is preferably oriented so that the opening in the skimmer faces outwardly from this corner area. The skimmer maintains this orientation by one or more novel and stable guide arrangements, yet none of which causes substantial friction by reason of moving up and down as the level of water changes in the tanks.
In view of the failure of the prior art to provide a small or compact, low cost, reliable skimmer that will skim a variety of oil films from the surface of a controlled environment, such as for example a hot tank, it is an object of the invention to provide an improved oil skimmer.
Another object of the present invention is to provide a skimmer which includes a submersible collection tube, and a contoured inlet to such tube formed in the side wall of a floating body.
Yet another object of the present invention is to provide a floating body which includes one or several floats in addition to the principal body member itself.
Still another object of the present invention is to provide a skimmer which includes at least one guide, and in some cases two guides, extending down through one of the floats (and elsewhere) to guide the skimmer in its vertical movement.
A further object of the present invention is to provide a floating skimmer which includes plural floats and a body as well as an inlet formed in the body, and whose vertical movement is determined by two guides which permit only vertical movement of the skimmer.
A still further object of the present invention is to provide a relatively fixed suction tube for oil and water which are made to accumulate in a collection tube.
An additional object of the present invention is to provide, in a different embodiment, a shallow collection cup and an extensible suction hose or the like for continuously withdrawing oil and water from the collection cup.
Another object of the present invention is to provide a collection tube which in one embodiment, is concentrically arranged with a suction tube, serving the dual function of acting as a guide for movement of the skimmer as well as collecting the mixture that accumulates therein.
Still another object of the present invention is to provide a skimmer and an appropriate fluid circuit for removing an oil-aqueous solution from the surface to be skimmed, depositing the mixture in a reservoir and returning the aqueous solution from the bottom of the reservoir to the hot tank, allowing the oil eventually to accumulate to a point where it substantially fills the reservoir.
Yet another object of the present invention is to provide a skimmer which is operable with a low-capacity intermittent suction pump.
Still another object of the present invention is to provide a skimmer with a horizontal opening for oil-aqueous solution, with the opening surrounded being by a flat shelf portion defined by contoured side walls.
A further object of the present invention is to provide a tank for aqueous solution and an oil film with a skimmer device which resides in one corner of the tank, preferably having the skimmer shrouded where it is protected from contact with parts which are immersed in the tank.
A still further object of the present invention is to provide a skimmer which is small, reliable and which may be produced at relatively low cost.
Another object of the present invention is to provide a skimmer having a readily accessible provision for adding or taking off weight in small increments to vary the skim gap precisely.
Yet another object of the present invention is to provide a skimmer with an inlet having vertical and near-horizontal surfaces making visualization of the skim gap easier and more reliable.
An additional object of the present invention is to provide a skimmer having a skim gap which is substantially independent of the temperature of the aqueous bath in which it is situated.
Another object of the present invention is to provide a skimmer whose effective thermal cubic expansion is essentially equal to that of bath so that variations in bath temperatures will have negligible effect upon the skim gap.
The invention achieves these and other objects by providing a floating skimmer having a body with a contoured inlet, a flat bottom shelf and a horizontally disposed opening, a reservoir disposed within the opening and a suction tube communicating with the reservoir, with the space between the aqueous level in the tank and the shelf being a carefully controlled skim gap.
The manner in which these and other objects and advantages of the present invention are achieved in practice will become more apparent when reference is made to the following description of the preferred embodiments of the invention and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.